Franz L. Wimmer

Bio: Franz L. Wimmer is an academic researcher from Cardiff University. The author has contributed to research in topics: Ring flip & Palladium. The author has an hindex of 6, co-authored 8 publications receiving 124 citations.

Inorganic optical activity

Abstract: The tris(pentasulphido)platinate(IV) compound (NH4)2[Pt(S5)3] has been crystallised in both a racemic and an optically active form.

Optically active co-ordination compounds. Part 43. Polysulphide complexes of platinum(IV)

Abstract: Brick-red [NH4]2[Pt(S5)3]·2H2O crystallises from the reaction mixture obtained on adding K2PtCl6 to an aqueous ammonium polysulphide solution. Addition of concentrated hydrochloric acid results in the separation of maroon [NH4]2[PtS17]·2H2O. The physical properties (solubility, i.r., Raman, and electronic spectra, X-ray powder pattern) of the complexes are described. The [Pt(S5)3]2– ion crystallises from solution as the racemate, whereas [PtS17]2– on crystallisation undergoes a second-order asymmetric transformation so that the solid contains an excess of the (–) enantiomer. The [Pt(S5)3]2– ion was resolved by forming diastereoisomers with [ RuL3]2+(L = 2,2′-bipyridyl or 1,10-phenanthroline). The circular dichroism spectra of both ions are described. The mechanism of racemisation is discussed.

Beyond Conventional N-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

Abstract: N atom, thus providing carbenes derived from pyrazolium, isothiazolium, and even quinolinium salts that contain a stabilizing heteroatom in a remote position (G-J in Figure 1). Recently, carbenes such as K, which are comprised of only one heteroatom and lack delocalization through the heterocycle, have been discovered as versatile ligands, thus constituting another important class of carbenes with low heteroatom stabilization. Both the synthesis of the organometallic complexes of these ligands as well as the (catalytic) properties of the coordinated metal centers generally show distinct differences, compared to the more classical NHC complexes, such as C2-metallated imidazolylidenes. This review intends to describe such differences and highlights the chemical peculiarities of these types of N-heterocyclic carbene complexes. It introduces, in a qualitative manner, the synthetic routes that have been established for the preparation of such complexes, covering the literature from the very beginning of activities in this area up to 2008. While specialized reviews on some aspects of the present topic have recently appeared,7 a comprehensive overview of the subject has not been available thus far. Rather than just being descriptive, the present account is mainly directed toward the impact of these still unusual metal-carbene bonding modes on the electronic properties and on the new catalytic applications that have been realized by employing such new carbene complexes. As a consequence of our focus on complexes with less-stabilized heterocyclic ligands, systems comprising acyclic carbenes have not been included, and the interested reader is, instead, referred to the pioneering and

Synthesis, structure, and properties of [Pt(II)(diimine)(dithiolate)] dyes with 3,3'-, 4,4'-, and 5,5'-disubstituted bipyridyl: applications in dye-sensitized solar cells.

Abstract: A family of [Pt(II)(diimine)(dithiolate)] complexes of general formula [Pt{X,X‘(CO2R)2-2,2‘-bipyridyl}(maleonitriledithiolate)] (where X = 3, 4, or 5 and R = H or Et) have been synthesized, spectroscopically and electrochemically characterized, and attached to a TiO2 substrate to be tested as solar cell sensitizers. A single-crystal X-ray structure showing a large torsion angle between the bipyridyl rings was determined for [Pt{3,3‘(CO2Et)2-2,2‘-bipyridyl}(maleonitriledithiolate)]·MeCN. The effect of changing the position of the bipyridyl substituents from 3,3‘ to 4,4‘ and 5,5‘ is discussed with reference to structural and electronic changes seen within the different members of the family of molecules. The first UV/vis/NIR spectroelectrochemical study of complexes of this general formula is discussed. All three complexes (where R = H) were tested as solar cell sensitizers, with the 3,3‘-disubstituted bipyridyl complex giving an intermediate dye loading value but superior photovoltaic performance to those ...

Combination of lacunary polyoxometalates and high-nuclear transition metal clusters under hydrothermal conditions: IX. a series of novel polyoxotungstates sandwiched by octa-copper clusters.

Abstract: The reaction of CuCl(2).2 H2O with trivacant Keggin polyoxoanions K8Na2[A-alpha-GeW9O34].25 H2O or K10[A-alpha-SiW9O34].25 H2O in the presence of 1,2-diaminopropane (dap), ethylenediamine (en) or 2,2'-bipyridine (2,2'-bpy) under hydrothermal conditions afforded five novel hybrid inorganic-organic octa-Cu sandwiched polyoxotungstates (POTs): H4[CuII8(dap)4(H2O)2(B-alpha-GeW9O34)2].13 H2O (1), (H2en)2[CuII8-(en)4(H2O)2(B-alpha-GeW9O34)2].5 H2O(2), (H2en)2[CuII8(en)4(H2O)2(B-alpha-SiW9-O34)2].8 H2O (3), [CuII(H2O)2]H2[CuII8-(en)4(H2O)2(B-alpha-SiW9O34)2] (4), and [CuII2(H2O)2(2,2'-bpy)2]{[CuII(bdyl)]2-[CuII8(2,2'-bpy)4(H2O)2(B-alpha-GeW9-O34)2]}.4 H2O (bdyl=2,2'-bipyridinyl)(5). Additionally, CuCl(2).2 H2O reacts with the mixture of GeO2, Na2WO(4).2 H2O, H2SiW12O(40).2 H2O in the presence of 2,2'-bpy and 4,4'-bpy under hydrothermal conditions leading to another novel mixed-valent octa-Cu sandwiched POT hybrid: [CuI(2,2'-bpy)(4,4'-bpy)]2[{CuI2(2,2'-bpy)2(4,4'-bpy)]2[CuI2CuII6(2,2'-bpy)2(4,4'-bpy)2(B-alpha-GeW9O34)2}].2 H2O (6). 1, 2, and 3 are discrete dimers constructed from two trivacant Keggin [B-alpha-XW9O34]10- (X=GeIV/SiIV) fragments and an octa-Cu cluster whereas 4 displays the 3D (3,6)-connected nets with (4.6(2))(4(2).6(4).8(7).10(2)) topology, which are built by octa-Cu sandwiched polyoxometalate building blocks through copper cation bridges. 5 is a novel 2D layer based on octa-Cu sandwiched POT clusters and [CuII2(bdyl)] units. Interestingly, the rollover metalation of 2,2'-bpy is firstly observed in the system containing the copper complex under hydrothermal conditions. 6 is a discrete mixed-valent octa-Cu sandwiched POT supported by two CuI-complexes [CuI2-(2,2'-bpy)2(4,4'-bpy)]2+ through 4,4'-bpy bridges, which constructs a novel dodeca-copper cluster. Notably, the octa-Cu cluster in 6 is mixed-valent and is different from those in 1-5. To our knowledge, 1-6 represent a rare family of POTs incorporating novel octa-nuclear transition-metal clusters in polyoxometalate chemistry. They were structurally characterized by FT-IR spectra, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. The magnetic properties of 1, 4, and 5 were quantitatively analyzed by the MAGPACK software package.

Polysulfide Complexes of Metals

Abstract: Publisher Summary Sulfide minerals were formed mostly hydrothermally from postmagnetic fluids; it appears remarkable that the formation of many ore deposits cannot be conclusively explained because of the very low solubility of the corresponding sulfide. Polysulfido complexes are interesting because of their structures and reactivity, and also because of their possible applications. They can—for example, be used to prepare sulfur rings of predetermined size and they are suspected to play a role in catalysis, particularly in hydrodesulfurization. Free polysulfide ions consist of sulfur chains. Complexes with S22– ligands show a remarkable variety of structures that result from the extension of the fundamental structural type Ia (side-on coordination) as well as IIa and IIb by using the remaining lone pairs of electrons (on sulfur) to coordinate additional metal atoms. Such coordination of additional metal atoms occurs for all three fundamental structural types (Ia, IIa, and IIb). Complexes with type II structures are presented in table along with their S–S distances and S–S vibrational frequencies. There are several routes for the synthesis of polysulfido complexes. Oxidative addition of elemental sulfur to a coordinatively unsaturated electron-rich metal is a convenient method for preparing Sn2– complexes.

“Rollover” cyclometalation – early history, recent developments, mechanistic insights and application aspects

Abstract: “Rollover” cyclometalation constitutes a special case among the well-known class of cyclometalation reactions. An overview is given that covers the very first description of this reaction type, as well as recent developments. In addition, not only condensed-phase experiments are reviewed, but also investigations based on mass spectrometric techniques, together with “in silico” studies using DFT-based calculations are considered. While the latter two methods allow for a detailed analysis of the intrinsic factors that affect the reaction mechanisms, consideration of all three regimes permits to develop a coherent mechanistic picture and to address the often noted gap between condensed- and gas-phase studies. Moreover, the quite unexpected reactivity of “rollover” cyclometalated complexes in gas-phase experiments, as well as potential applications, e.g. in synthetic procedures, are discussed in some detail.